Door frame piece (4)
I believe the answer is:
jamb
'door frame piece' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for jamb that I've seen before include "Door, window side post" , "Side post of a doorway" , "Vertical side of a doorway" , "Door sidepiece" , "bit on the side?" .)